Exclude custom post type from search by custom field value?

Question

I've been unable to find anything on how to do this, or if it's even possible.

What I want to do is not display results of search in custom post type "resources" on which "resource_usertype" (key) is not "Public" or "Students" or "Alumni" (values).

Or maybe a better way to say it is to only display search results in which values of "resource_usertype" are "Public", "Students", or "Alumni".

Answer 1

You need to implement a hook for pre_get_posts filter, in which you can set what you need. Pay attention that you should change only search query, so you have to check if is_search() method returns true. The hook should look like this:

add_filter( 'pre_get_posts', 'wpse8170_pre_get_posts' );
function wpse8170_pre_get_posts( WP_Query $query ) {
    if ( $query->is_search() ) {
        $query->set( 'post_type', array( 'resources' ) );
        $query->set( 'meta_query', array(
            array(
                'key' => 'resource_usertype',
                'value' => array('Public', 'Students', 'Alumni'),
                'compare' => 'IN',
            )
        ) );
    }

    return $query;
}

Answer 2

It's perfectly possible!

$args = array(
   'post_type' => 'resources',
   'meta_query' => array(
       array(
           'key' => 'resource_usertype',
           'value' => array('Public', 'Students', 'Alumni'),
           'compare' => 'IN',
       )
   )
 );
 $query = new WP_Query($args);